Thru Hull Transducer

Old 11-18-2002, 11:08 AM
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Default Thru Hull Transducer

What do you think is the best sealant to use to install my bronze thru hull transducer and urethane fairing block to a fiberglass hull?
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Old 11-18-2002, 11:20 AM
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Default Thru Hull Transducer

I would use 3M 5200 on the fairing block & tranducer below the water line for strength and 3M 4200 inside the hull around the hole and locking nut so it can more easily be removed.
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Old 11-18-2002, 01:00 PM
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Default Thru Hull Transducer

I only use 5200 where its adhesive properties are needed (unless its all I have laying around). For sealing a thru hull adhesion isn't important, just making a gasket really. So I use virtually any silicon sealer that is handy. Actually I don't want the adhesive capabilty of 5200 in that application and never use it there if I have a choice.

As long as I'm here I guess I should tell you the trick (method) to seal on in. Mount it in place and use plenty of goop (whatever sealer you end up using. Of course you're gonna have someone on the inside and someone on the outside. So here's the deal. Liberly coat the top of the fairing block and the top of the transducer. Slip the fairing block over the transducer stem and then stick the stem up through the hull. The person on the inside should have alread put down a good bed of sealer on the hull (clean with acetone first) where the top half of the fairing block is going to go. When the stem stick through put a ring of sealer around right where it comes through the hull. Put the top half of the fairing block down into the bed of sealer. Now screw down the nut - by hand only. Snug up the nut real good with fingers, no more. Now, from under the boat check the level real well. Get it perfect along with whatever degree of forward tilt you are going to use. Walk away. Don't come back for a day (three days if you use 5200). When you come back take a pair of channel locks and tighetn down the stem nut - don't see how tight you can possibly get it, just get it nicely tightened. That's it.

What you have done is made a gasket out of the sealer. You did not tighten down the nut on day one because if you had it would have squeezed out most of you sealer. So you let it set up first and then came back and tightened up later. This will give you a waterproof seal and it doesn't matter at all what kind of sealer you used. For whatever its worth my favorite for the job is West Marines house brand of sealer, called Multi Caulk Sealer.


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Old 11-20-2002, 03:12 PM
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Default Thru Hull Transducer

I wouldnt trust anything but 5200 below the waterline... if you hit something underwater, atleast the 5200 has great resiliance and holding power, whereas a silicone seal is very easy to break in such an application. I would use 5200 on the inside as well, but thats a matter of choice- its almost a matter of fact to use 5200 below the waterline, the stuff never fails. P.S. use alcohol to remove the 5200 from your hands, i havent found anything besides rubbing alcohol and acetone that work and acetone dries out your skin and ive heard it is absorbed thru the skin and attacks the liver. Who knows, im not a doctor. Good luck.
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Old 11-20-2002, 05:50 PM
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Default Thru Hull Transducer

3M 101 is what I use and recomment for thruhull fittings. It cures underwater, doesn't have the tenacity of the 5200. I ask; why do you want to GLUE underwater fittings to the boat?? They are already held on with relatively huge hardware...
Can you tell i just fought with removing shaft struts on an inboard that were 5200 onto the hull. Like the 8 3/8" thru bolts were too weak?? You need a great seal, not a replacement for hardware...

*I wouldn't expect agreement on this topic or most others...
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Old 12-06-2002, 03:40 AM
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Default Thru Hull Transducer

Diver Dave, I must remind you that up in the northeast the random telephone pole hiding in the water floating is not uncommon... driftwood is a killer because the water is so dark, you just cant see it. No hardware is tough enough to take a giant log hit to the underside of the boat, the 5200 just gives you that little extra edge of a fighting chance. I wouldnt leave shore without using it just because i was too much of a sissy to remove anything held on by it... by the way, they sell a product that breaks it down for easy removal. See ya.
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Old 12-06-2002, 06:12 PM
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Default Thru Hull Transducer

I'm starting to lean toward using 3M 101 like Diver Dave suggests. According to what I've read the 101 cures upon contact with water. If you hit something there is still wet 101 around the hole. Once water gets to the wet 101 it will reskin and again form a seal. This way if you sell your boat and want to keep your electronics or need to replace a transducer that has gone bad it's much easier to remove and clean-up than it would be if you used 5200.
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Old 12-06-2002, 11:43 PM
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Default Thru Hull Transducer

Im a believer in lifecaulk,it cures underwater,Ive never had a failure in 28 years useing this stuff.It turns to rubber.

Tim,25'Skip,Reel Hungry
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